This invention relates to the extraction of data from an array of detectors arranged in rows and columns, such as an array of detectors of infrared radiation in an imaging system, and, more particularly, to the use of frequency multiplexing and frequency modulation for communicating data over an optical fiber communication link, this being particularly advantageous for coupling imaging data out of the cold (Dewar) region of an infrared sensor.
Imaging systems constructed of large arrays of detectors are employed in various situations in which it is desired to attain data of a subject electronically by sampling the intensity of radiation in a field of radiation emanating from the subject. A detector element is located on each of numerous sites of a detector array located at the focal plane at which the field of radiation is brought to a focus. Each detector element provides data as to one pixel of an image of the subject. The field of radiation may be swept past the detector array by use of a scanning mirror or, alternatively, the detector elements may be arranged in a two-dimensional array of rows and columns capable of extracting two-dimensional imaging data from a stationary field of radiation. By way of example, there may be 1000, 10,000 or more detector elements in the detector array. In the case of an infrared imaging system, wherein each of the detector elements is a sensor of infrared radiation, it is the practice to construct the detector array within a housing which maintains a cold temperature, the housing having a viewing port through which the incident radiation field enters the housing to be focused upon the detector array. All the data provided by the array of detector elements must be communicated via some form of communication link through a wall of the housing to an external warmer environment wherein the data is processed by filtering or image enhancement, by way of example, to be stored or displayed.
A problem arises in that there are numerous situations wherein the image data changes rapidly, such as in the case of the viewing of a moving object, in which case the many detector elements must be interrogated frequently to update the image data. However, in view of the many detector elements, a frequent updating of the data provided by each of the numerous detector elements presents a considerable burden on the communication link connecting the detector array to the image processing circuitry. As a result, there is a need for a form of communication link which is capable of handling the higher data rates and which is readily connected to the detector elements, even in the case wherein the elements are closely spaced for a high-resolution image.